The properties required of the nonaqueous electrolyte solutions used in lithium secondary batteries have become more and more rigorous with each passing year. The desire for an electrolyte solution that can be used at high voltages reflects one such property requirement.
As a method that solves this problem, the use of a fluorinated ethylene carbonate (EC) as a component of the solvent for the nonaqueous electrolyte solution has been proposed in order to increase oxidation resistance, inhibit dendrite formation, and improve the battery characteristics at high voltages (Patent References 1 to 7).
These patent references disclose the following as the fluorinated ethylene carbonate: fluoroethylene carbonates provided by replacing the hydrogen in ethylene carbonate with fluorine, e.g., monofluoroethylene carbonate (FEC) and di- to tetrafluoroethylene carbonates; mono(fluoroalkyl) substitutes for ethylene carbonate, e.g., monotrifluoromethylethylene carbonate (CF3EC), mono(fluoroalkyl)ethylene carbonates (RfCH2-EC and Rf2CH-EC), and monofluoroalkyl ether ethylene carbonates (RfCH2OCH2-EC); and 1,2-di(fluoroalkyl) substitutes for ethylene carbonate, e.g., 1,2-ditrifluoromethylethylene carbonate.
Patent Reference 1: Japanese Patent Application Laid-open No. 2008-108689
Patent Reference 2: Japanese Patent Application Laid-open No. 2009-110886
Patent Reference 3: Japanese Patent Application Laid-open No. 2007-250415
Patent Reference 4: Japanese Patent Application Laid-open No. 2006-294414
Patent Reference 5: Japanese Patent Application Laid-open No. 2000-195544
Patent Reference 6: Japanese Patent Application Laid-open No. 2007-188873
Patent Reference 7: Japanese Patent Application Laid-open No. H8-306364